This paper presents a new design for wireless power transfer (WPT) systems using asymmetric structures for the transmitter (TX) and the receiver (RX), and the TX/RX are constructed using spiral-strips defected ground structure (DGS) resonators. The proposed spiral-strips DGS resonator overcome the problem of low self-inductance that encountered by H-shape DGS resonator in [1, 2], so that the proposed WPT system that employs the proposed spiral-strips DGS resonators has better efficiency and higher power transmission distance. Design methodology of the proposed WPT system are formulated and fabricated. The measurement results show a WPT efficiency of 78% at a transmission distance of 40 mm with the TX and RX areas of 50 x 50 mm2 and 30 x 30 mm2, respectively.